By Amy Vega - June 12, 2014
SPD and Inhibition Control
I recently discovered this paper by Koziol et al that was published online in the journal Cerebellum
in 2011. It is extremely interesting and convincing so I wanted to share it with you as so many of you encounter children with Sensory Processing Disorder (SPD) in clinical and educational settings, and so many children with SPD are demonstrating improvement with Interactive Metronome (IM) training. This paper is a good starting point to better understand the possible biological underpinnings of SPD, why we see it so often as a co-morbidity with other disorders like ADHD and Autism, and why IM training appears to be so helpful.
As many as 80% of children with developmental disorders display symptoms of SPD. SPD very rarely occurs in isolation. The authors suggest this co-morbidity occurs because the symptoms of SPD overlap with several developmental disorders, in which the same neural networks and neurobiologic mechanisms are implicated. These include ADHD, Autism Spectrum Disorders, Developmental Coordination Disorder, and others. There has been much controversy over the specific terminology and neuroanatomical correlates for what has been referred to as sensory integration disorder, sensory processing disorder, and sensory modulation disorder. The authors of this paper appear to be determined to foster deeper thought and more research as they suggest several anomalous neuroanatomical interactions that likely contribute to problems with sensory processing, specifically communication between the neocortex, basal ganglia, and cerebellum. That aberrant communication within and between several neural networks results in a child’s difficulty with selecting what sensory information in the immediate environment to pay attention to and what to disregard, and regulating the “force” with which sensory information is experienced. They argue that “sensory seeking” children are not seeking sensory experiences that they are lacking, but rather that they are stimulus-bound and lack appropriate self-regulation and impulse-control as they are unable to appropriately gate or select what stimuli in their environment they should pay attention to. It is a problem with “inhibition.”
The posterior regions of the neocortex are exquisite sensory processors and the anterior neocortical regions are elegant motor programmers. Accordingly, the human being can perceive the world and develop and execute specialized motor programs like no other species. This higher-order and flexible range of adaptation generates enormous, complex behavioral possibilities so that the individual is almost constantly confronted with the need to select that to which to attend and the behavior in which to engage. In other words, the price we pay for our highly developed neocortex and its associated advanced cognitive and behavioral possibilities is the demand to contend with the overwhelming selection problem it generates.
The authors postulate that sensory processing anomalies are subtle indicators of deficits in “executive control.” The ability to be purposeful and self-direct behavior not only relies upon attention and working memory, but also upon the person’s capacity for inhibition. Self-restraint, or the ability to NOT respond to an immediate stimulus, but to delay gratification, is prerequisite to the development of metacognitive executive function, cognitive control, and self-regulation. Think of inhibition as the gap of time between stimulus and response as an opportunity to “think” before acting. This ability develops into working memory and higher order thinking like planning, anticipating, and goal-setting…extremely important skills for success in academics and life in general.
Another very important concept discussed in this paper is the role of “adaptation” in sensory processing. Humans are driven to survive, and survival is achieved through adaptive interactions with our environment that are based upon movement, perception, and mental representations as we plan and visualize the outcome of our plans. The more a behavior is executed, the more it becomes automatic or routine, and can be completed spontaneously without conscious cognitive control. However, intermittently, we encounter a change in our environment that requires problem-solving or a new plan, in which case we must actively recruit effortful cognitive control in order to learn and adapt to the new situation.
Engaging in automatic behaviors recruits an interaction of brain structures that run on the basis of acquired or learned associations. These brain regions include the motor cortices, the basal ganglia, and the cerebellum. Changing or modifying behaviors and learning new behaviors involves the interaction of different brain structures and regions, including the prefrontal cortex, the SMA, and subcortical structures, as will be described in subsequent sections of this paper. The brain serves adaptation by conserving resources. Developing effective behaviors to meet the challenges presented by novel or new situations initially requires effortful cognitive control. The more a behavior is practiced, the less cognitive effort its performance requires and the more automatically it can be generated. Automating frequently occurring behaviors allows the brain to conserve energy, while it simultaneously frees up the conscious cognitive control system to manage or “problem-solve” the next experience of novelty. The brain functions according to this principle of novelty-routinization. It essentially takes that which is novel and makes it familiar. This model of brain functioning requires interactions between the neocortex, the basal ganglia, and the cerebellum. These interactive processes are at a premium in child development specifically because the pediatric population, by definition, is in the process of acquiring adaptive skills to use to interact effectively with the environment. Child development proceeds according to the increasing control a child can exercise over the motor system.
Interactive Metronome® training encourages synchronous communication between key neural networks responsible for sensory processing. While initially, IM training requires much cognitive effort, as learning and synchronization improve, cognitive and motor skills become automatized so that cognitive resources are conserved and “adaptation” can occur. Additionally, IM training facilitates inhibition. According to an independent blind, randomized, controlled study U.S. Defense & Veteran’s Brain Injury Center (DVBIC), soldier’s who received IM training demonstrated substantial improvements in inhibition, attention, working memory, and executive functions with large effect sizes. If sensory gating and inhibition are at the heart of SPD, this may help explain why so many children with SPD demonstrate far less auditory/tactile oversensitivity and fewer “sensory seeking” behaviors following IM training.